In one aspect this invention relates to pyroelectric materials. In a further aspect, this invention relates to pyroelectric polymeric film materials. In yet another aspect, this invention relates to a method for copying a graphic representation using uniformly poled pyroelectric materials.
It is well known that the dipoles of a pyroelectric material, e.g. polyvinylidene fluoride film, which is biaxially oriented by the method of production, can be permanently poled by heating the material above a dipole-orienting temperature and then cooling the material in the presence of the electric field, see Bergman et al, Applied Physics Letters, Vol. 18, No. 5, March 1, 1971, p. 203-204.
Also known is the use of a plurality of pyroelectric-photoconductive crystals on a supporting substrate to form copies. The crystals are heated then exposed to a light source through a pattern which selectively heats the crystals, forming a charge, and simultaneously the photoconductive effect selectively drains away the charge produced. When the light source is removed, a differential charge remains which will attract toner powder, see U.S. Pat. No. 3,713,822.